Optical Transport Network (OTN) is a physical layer protocol (Layer 1) for Time Division Multiplexing (TDM) providing transport, multiplexing, switching, management, supervision, and protection/survivability of optical channels carrying client signals. OTN is defined inter alia in ITU-T Recommendation G.709 “Interfaces for the Optical Transport Network (OTN),” (02/12), the contents of which are incorporated by reference. With respect to protection, OTN deployments can support various techniques for path protection which switch OTN channels or lines responsive to a failure in the OTN network which affects the channels or lines. Path protection is dedicated protection in the OTN network with a working and a protection channel (also referred to as active and standby, primary and backup, or combinations thereof). One exemplary type of path protection is Subnetwork Connection Protection (SNCP). Thus, path protection can provide 1+1 Automatic Protection Switching (APS) protection of channels in the OTN network or a non-OTN network, on the line-side to protect against failures in the OTN network or the non-OTN network. Additionally, services can also include client-side protection such as 1+1 client protection which is meant to protect against failures on client-side modules or hand-offs from a client network. Those of ordinary skill in the art understand that path protection is also available in SONET, SDH, Ethernet, etc., and OTN is described herein for illustration purposes.
With both path protection in OTN and client-side protection on the associated clients, there is a scenario where a client-side switch, such as due to a failure of a client module or a fault in the client network, can lead to the detection of an anomaly in OTN causing path protection undesirably. This can be referred to as a sympathetic switch in OTN when client-side APS switches. Of course, this causes problems in traffic between client-side ports and OTN line ports. Conventional approaches to rectify this problem include implementing a hold-off time on the OTN side whenever there is a client-side switch. Disadvantageously, this can lead to protection switch times in excess of 100 ms, which is the exact opposite objective of path protection which strives for sub-50 ms protection switch times.